Throwing a couple of ideas out:
.303 British case trimmed to 2" even, necked to 6 or 6.5mm (no reason it couldn't be done smaller, too, but those are the two that came to mind immediately) with shoulder blown out to say 25 degrees, maybe make the body just below the shoulder .450" (it's .455" at the base and .401" just below the shoulder on original cases).
6.5x50mm Japanese trimmed to 1.775", necked to ..224" or .257", 25 degree shoulder and .445" body below the shoulder (.451" at the base and .409" just below the shoulder for the original).